tun: fix premature POLLOUT notification on tun devices

BugLink: http://bugs.launchpad.net/bugs/1675032
[ Upstream commit b20e2d54789c6acbf6bd0efdbec2cf5fa4d90ef1 ]

aszlig observed failing ssh tunnels (-w) during initialization since
commit cc9da6cc4f56e0 ("ipv6: addrconf: use stable address generator for
ARPHRD_NONE"). We already had reports that the mentioned commit breaks
Juniper VPN connections. I can't clearly say that the Juniper VPN client
has the same problem, but it is worth a try to hint to this patch.

Because of the early generation of link local addresses, the kernel now
can start asking for routers on the local subnet much earlier than usual.
Those router solicitation packets arrive inside the ssh channels and
should be transmitted to the tun fd before the configuration scripts
might have upped the interface and made it ready for transmission.

ssh polls on the interface and receives back a POLL_OUT. It tries to send
the earily router solicitation packet to the tun interface.  Unfortunately
it hasn't been up'ed yet by config scripts, thus failing with -EIO. ssh
doesn't retry again and considers the tun interface broken forever.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=121131
Fixes: cc9da6cc4f56 ("ipv6: addrconf: use stable address generator for ARPHRD_NONE")
Cc: Bjørn Mork <bjorn@mork.no>
Reported-by: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Reported-by: Jonas Lippuner <jonas@lippuner.ca>
Cc: Jonas Lippuner <jonas@lippuner.ca>
Reported-by: aszlig <aszlig@redmoonstudios.org>
Cc: aszlig <aszlig@redmoonstudios.org>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index bfabe180053e414dee777e0e56b24eceef05c918..cdf6339827e67dfc83b11caa715bd0319c2f6d7f 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -819,7 +819,18 @@ static void tun_net_uninit(struct net_device *dev)
 /* Net device open. */
 static int tun_net_open(struct net_device *dev)
 {
+       struct tun_struct *tun = netdev_priv(dev);
+       int i;
+
        netif_tx_start_all_queues(dev);
+
+       for (i = 0; i < tun->numqueues; i++) {
+               struct tun_file *tfile;
+
+               tfile = rtnl_dereference(tun->tfiles[i]);
+               tfile->socket.sk->sk_write_space(tfile->socket.sk);
+       }
+
        return 0;
 }
 
@@ -1101,9 +1112,10 @@ static unsigned int tun_chr_poll(struct file *file, poll_table *wait)
        if (!skb_array_empty(&tfile->tx_array))
                mask |= POLLIN | POLLRDNORM;
 
-       if (sock_writeable(sk) ||
-           (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
-            sock_writeable(sk)))
+       if (tun->dev->flags & IFF_UP &&
+           (sock_writeable(sk) ||
+            (!test_and_set_bit(SOCKWQ_ASYNC_NOSPACE, &sk->sk_socket->flags) &&
+             sock_writeable(sk))))
                mask |= POLLOUT | POLLWRNORM;
 
        if (tun->dev->reg_state != NETREG_REGISTERED)